1. Field of the Invention
The invention relates to thermoformed, three dimensional wiring modules containing high density conductive wiring.
2. Description of the Related Art
Multilayer wiring modules, e.g. circuit boards, circuit substrates or circuit memory cards, are known in the electronics industry as a base to provide conductive paths among various electronic components present in a computer system. The common modules comprise a plurality of layers which are fabricated to contain a conductive wiring pattern on one or both of the layer surfaces, including a number of electrically conductive vias formed through at least some of said layers such that when a plurality of such layers are laminated together in appropriate alignment using heat and/or pressure, useful electrically conductive interlayer pathways are formed within the module. A typical planar module formed from layers of thermoplastic polymer materials is disclosed in U.S. Pat. No. 5,259,110, the complete disclosure of which is incorporated herein by reference.
In some applications, it is desirable to provide thermoformed, three dimensional modules such as, for example, disclosed in U.S. Pat. Nos. 4,528,748 and 5,264,061. Three dimensional modules are particularly desirable for use as interchangeable computer circuit cards. Circuity may also be present in the molded plastic housing of small computers such as the computer case of a lap top, which housing itself can then serve as a circuit board and interconnect, providing a lighter weight and more efficient computer package.
It is extremely difficult to form precise and desirably dense circuit patterns on three dimensional, non-planar substrates by conventional pattern-forming technology such as thin film lithography, electroless plating or screen printing techniques, because of light and mechanical distortion problems which arise when dealing with a non-planar surface.
An obvious solution to this problem with respect to modules fabricated from thermoplastic polymers would be to first construct the multilayer interconnect system in the planar state and then thermoform the defined module into the desired three dimensional shape. However, the thermoforming process puts undue stress on the internal wiring present in the module, particularly wiring present on the outer layers of the module opposite the inner angle of bend. This can lead to breakage or shorting of the circuit in these regions as consequence of stress bending encountered in the thermoforming process.